1. Technical Field
The present invention generally relates to integrated circuits and in particular to thermal isolation in integrated circuits.
2. Description of the Related Art
When two or more electronic devices with integrated circuits are stacked in a vertical plane, heat that is generated by one or more of the devices is able to couple to the other devices. Coating the surface of the electronic device(s) with a high thermal insulating material may provide improved isolation between heat sources and heat sinks with differing loads. Improved heat isolation is achieved by mitigating the propagation of heat to critical and/or temperature sensitive components or circuits.
Conventional materials in use for thermal isolation today are inadequate for applications in high thermal density environments. The materials deteriorate with time and exposure to steady state high temperatures and environmental conditions that exist in many high power and high performance applications. Also, based on thermal expansion characteristics, density, and thickness, conventional materials experience mechanical failures such as cracks and delamination from surfaces to which these materials were initially bonded. These mechanical failures reduce and sometimes nullify the effectiveness of the conventional materials as a thermal isolator or insulator.
When bonding two independent circuits together to create electrical connections between them or to create vertical integration, thermal isolation is very important. Materials used to bond two IC substrates together are applied to the area between the circuit substrates. The filler materials (either die attach or underfill materials) are not designed specifically for high thermal density isolation.
The drawbacks of bonding two substrates with high heat generating circuits include compound heat generation and localized heating of one or more of the adjoining surfaces. Efficient coupling of heat may lead to thermal runaway of one or more of the independent circuits on the substrate due to the additive heat sourced by one or more adjacent or proximate devices. Thermal runaway may be also caused by structural, mechanical and electrical failures due to differences in thermal coefficients of expansion and large thermal gradients across the device, as a result of the different characteristics of bonding and substrate materials.